Method for monitoring the configuration of an upwardly drawn ribbon of glass

ABSTRACT

In the processing of sheet material by drawing a ribbon of the material upwardly, a method and apparatus for monitoring deflections experienced by the material out of the vertical plane along which it is normally drawn by providing sensing components near, and normally out of contact with, opposite faces of the ribbon and by arranging the components to produce an output indication in response to a change in a physical condition of the region adjacent the component due to such deflection.

United States Patent [1 1 Toussaint et al.

METHOD FOR MONITORING THE CONFIGURATION OF AN UPWARDLY DRAWN RIBBON OF GLASS Robert Toussaint; Elzo Mulder, both otl sll N th ans Assignee: Glaverbel S.A., Brussels, Belgium Filed: Aug. 17, 1972 Appl. No.: 281,485

Related US. Application Data Division of Ser. No. 71,029, Sept. 10, 1970.

Inventors:

Foreign Application Priority Data Sept. 10, 1969 Great Britain 44,650/69 July 29, 1970 Great Britain 36,764/70 US. Cl 65/29, 65/90, 65/158,

65/159, 65/160 Int. Cl C031) 15/04 Field of Search 65/29, 90, 91, 193,

[ Nov. 20, 1973 [56] References Cited UNITED STATES PATENTS 2,972,210 2/1961 Broman et a1. 65/29 3,304,615 2/1967 Ward et al. 33/143 3,482,954 12/1969 Wing Yuen.......... 65/158 3,539,324 11/1970 Terakado et 65/158 3,222,151 12/1965 Schreffler 65/29 Primary ExaminerArthur D. Kellogg Attorney-Spencer & Kaye [57] ABSTRACT In the processing of sheet material by drawing a ribbon of the material upwardly, a method and apparatus for monitoring deflections experienced by the material out of the vertical plane along which it is normally drawn by providing sensing components near, and normally out of contact with, opposite faces of the ribbon and by arranging the components to produce an output indication in response to a change in a physical condition of the region adjacent the component due to such deflection.

9 Claims, 11 Drawing Figures PAIENTEBNBY 20 1975 SHEET 5 BF 7 Fig.6.

lllllll I Fig.7.

METHOD FOR MONITORING THE CONFIGURATION OF AN UPWARDLY DRAWN RIBBON OF GLASS CROSS REFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 71,029, filed Sept. th, 1970 now US. Pat. No. 3,725,027.

BACKGROUND OF THE INVENTION This invention relates to processes and apparatus for the manufacture of sheet glass.

Sheet glass is customarily produced by drawing molten glass in a continuous ribbon from a bath of molten glass contained in a tank and by then allowing the drawn glass to cool as it travels away from such bath.

The ribbon is drawn at a constant speed so as to subject the still molten glass of the ribbon in the drawing chamber to uniform drawing tension. This is necessary because any change in the dynamic equilibrium of the upwardly moving ribbon of molten glass in the drawing chamber may have very serious adverse effects on the quality of the resulting glass product so that the ribbon must be kept under virtually constant observation. If the ribbon of glass should break while cooling, the glass below the break may, unless it is caught in time, slip back into the bath of molten glass in the drawing tank. This is highly undesirable because the re-establishment of the ribbon, as well as of the equilibrium conditions, is a major task and takes appreciable time during the whole of which no useful production occurs.

SUMMARY OF THE INVENTION It is a primary object of the invention to prevent such a situation from occurring.

Another object of the invention is to provide an automatic indication that such a situation is occurring, or is about to occur.

A further object of the invention is to utilize such indication for automatically gripping the ribbon in order to prevent it from falling back into the bath.

It has been observed that a change in the dynamic equilibrium conditions, due to some fault either in the drawing machine or the glass, is usually immediately followed by buckling of the glass ribbon in a region where the glass is in molten state. This buckling occurs in the event of breakage of the cooling ribbon, as above referred to, and in the event of a sudden decrease in the drawing rate. The present invention makes use of this phenomenon to provide an automatic indication of the occurrence of the fault.

According to the invention, a glass ribbon is drawn from a bath of molten glass upwardly between components which are located near to, but out of contact with opposite faces of the ribbon, and form part of an indicator system which yields a signal in the event that the portion of the ribbon between the components moves by at least a certain minimum distance out of a predetermined plane.

Preferably the indicator system components located adjacent opposite faces of the ribbon form part of an electric indicator circuit which produces signals that can be instantly effective, with or without amplication, to initiate warning and/or control operations.

The indicator system may yield a signal in the event of actual contact of the glass ribbon with the one or more indicator system components located to one side of the drawn glass ribbon. This arrangement is conducive to a very positive operation of the indicator system. For realizing this advantage, the indicator system components located on opposite sides of the drawn glass ribbon may, e.g., be electrodes or switch arms forming part of an electric indicator circuit which produces a signal in the event that an electric current path is established due to the glass ribbon contacting an electrode or displacing a switch arm, as the case may be. If switches are employed, they may be extremely sensitive microswitches which respond to the slightest contact.

As an alternative, the indicator system may produce a signal in the event that the spacing of the glass ribbon from one or more indicator system components located on either side of the glass ribbon path becomes reduced or increased by more than a predetermined value, which can be minimal and merely dependent on the sensitivity of the system. The advantages of this arrangement is that contact of the indicator system components by the glass ribbon can be avoided so that fouling of such components by molten glass can be prevented, thus eliminating one cause of impairment of the functioning of the system. This advantage can be realized in an electrical indicator system by making use of components in the form of electrodes which form capacitors with the glass ribbon and by detecting changes in the capacitances of such capacitors, or by providing components in the form of fluid discharge devices which continuously discharge streams of fluid, e.g., air, against opposite sides of the glass ribbon and by detecting changes in the fluid flow conditions, e.g., changes in fluid pressure, which occur in the devices on respectively opposite sides of the ribbon in consequence of the ribbon buckling and therefore moving nearer to the fluid discharge device or devices on one side of the ribbon and further away from the other discharge device or devices.

The components located near to opposite faces of the ribbon are preferably located at a level near to the surface of the molten glass bath since buckling of the glass ribbon usually first becomes noticeable in this region.

The indicator system components located near to the opposite faces of the ribbon may be connected to a common indicator device or they may be connected to individual indicator devices.

Preferably the signal yielded by the indicator system in the event of buckling of the glass ribbon is used to actuate a device for gripping the ribbon of glass to prevent it from falling in the event that the buckling is due to breakage of the ribbon. This feature affords the important advantage of preventing the serious disturbances which occur to the plant if the ribbon falls.

By way of example, the output signal may be used for causing actuation of a mechanism whereby one or more gripping rollers are displaced into contact with the glass ribbon. The expression indicator system thereby includes a system in which the signal produced in the event of buckling of the glass ribbon is, for example, a mechanical movement or an electric current or voltage which exerts some form of automatic control on the machine. However, irrespective or whether such a control is exercised, it is preferable for the indicator system to include a visual or audible warning device which immediately alerts the operating personnel to the occurrence of the fault.

As has already been mentioned, buckling of the ribbon may not always be due to ribbon breakage. Buckling also may occur due to a fault resulting in reduction of the glass drawing speed, and the actuation of a warning device is useful for drawing immediate attention to this fault and enabling corrective action to be taken before a more serious situation develops.

The invention can be used in the drawing of glass upwardly through a vertical drawing tower, as in the case of the Pittsburgh process. In such process it is customary to provide, at the bottom end of the tower section, at least one pair of rollers which do not grip the glass ribbon during normal production but by which the glass ribbon can be gripped in the event the ribbon should break at a higher point in the tower section. Normally one roller of each pair is a fixed roller, the other being a floating roller which can be moved into contact with the glass ribbon in the event of a warning signal being given by the man on duty at the observation window of the drawing machine. The indicator system employed in accordance with the invention may operate automatically to displace the floating rollers in such a Pittsburgh type machine.

The invention is useful not only with systems for drawing glass upwardly through a vertical drawing tower, but can also be used with systems drawing glass by the Colburn type drawing process in which the ribbon of glass is drawn upwardly from the bath of molten glass and passed over a bending roller from which the ribbon continues its movement in a substantially horizontal direction. In such a process, the signal yielded in the event of buckling of the ribbon can also operate a roller or rollers or some other form of device or devices for gripping the ribbon at a portion between the molten glass bath and the place at which the breakage responsible for the buckling of the ribbon normally occurs.

The invention also includes glass drawing apparatus including means for holding a bath of molten glass and means for drawing a ribbon of glass upwardly from such bath, and provided with an indicator system including components spaced from, and on opposite sides of, the correct vertical drawing path of the ribbon, the system containing means which register when the portion of the ribbon passing between the components is displaced by at least a certain minimum distance from its correct path in a direction towards at least one component and which causes emission ofa signal indicative of that situation.

Preferably the indicator system contains an electric indicator circuit giving an instant response in the form of an output current or voltage which may be amplified to give the required signal.

The sensing components adjacent the correct vertical drawing path of the ribbon are advantageously in the form of electrodes connected to a voltage source.

According to one type of indicator system employing sensing electrodes as the sensing components, a predetermined deflection of the portion of the ribbon passing between the electrodes is registered by means which detects the passage of an electric current from at least one electrode to ground via the glass ribbon. The flow of such a current indicates that the glass ribbon has moved into contact with one of the electrodes.

According to another type of system employing sensing electrodes as the components adjacent the correct drawing path, a predetermined displacement of the portion of the ribbon passing between the electrodes is registered by means which detects variations in the capacitance of at least one capacitor constituted jointly by one electrode, the glass ribbon and the gas therebetween, the gas forming the dielectric of the capacitor. In this case the signal indicative of the fault is emitted before any contact of the glass with an electrode and responsive action can take place so that in fact no such contact ever occurs.

When using a capacitance type indicator system it is advantageous for the system to include means which registers differences between variations in the capacitances of the capacitors at opposite sides of the ribbon path so that incidental capacitance variations due to factors other than displacement of the ribbon from its correct path are of no consequence.

In yet a further type of indicator system, the sensing components are switch arms which are displaced when contacted by the glass, causing flow of an electric indi-.

cating current.

Yet a further type of indicator system includes means for directing streams of air or other fluid against opposite faces of the glass ribbon through discharge components located on opposite sides of the ribbon path, and means which respond, e;g., by measuring fluid pressure, to variations in fluid flow through a component due to displacement of the glass ribbon towards or away from such component. The system may include an instrument which yields an electrical signal responsive to any such registered variation. Again, it is advantageous for the instrument to register differences in variations in the fluid flow through opposed components so that difference common to the fluid discharges on opposite sides of the ribbon and due to factors other than displacement of the ribbon from its correct path are of no consequence.

Preferably the indicator system components on opposite sides of the ribbon path are located at a level near to the level reached by the molten glass bath when the apparatus is in use.

According to a preferred feature of the invention, the indicator system includes ribbon gripping means actuated by the signals indicative of buckling of the glass ribbon and serving to grip the ribbon and prevent it from falling into the molten glass bath in the event that the buckling is due to breakage of the ribbon. Preferably the gripping means consist of one or more gripping rollers which can be displaced to come into contact with the glass ribbon and which are constructed to support the ribbon when brought into engagement therewith.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevational view of part of a sheet glass production plant provided with one embodiment of the invention.

FIG. 2 is a detail plan view, on a larger scale, showing the mounting of certain components of the control system shown in FIG. 1.

FIG. 3 is a cross-sectional elevational view of an electrode assembly used in the plant of FIG. 1.

FIG. 4 is a circuit diagram of one embodiment of an indicator and control system according to the invention.

porating another type of indicator and control system according to the invention.

FIG. 7 is a cross-sectional view, on a larger scale, of an electrode assembly used in the plant of FIG. 6.

FIG. 8 is a circuit diagram of part of the indicator and control circuitry used in the system of FIG. 6.

FIG. 9 is a cross-sectional plan view of part of the drawing chamber of another glass drawing plant incorporating a further type of indicator and control system according to the invention.

FIG. is a diagrammatic cross-sectional elevational view of part of another sheet glass production plant provided with one embodiment according to the invention.

FIG. 11 is a diagrammatic cross-sectional plan view of another type of indicator and its assembly according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows part of a Pittsburgh type glass drawing machine and FIGS. 2 and 3 show further details of the control system according to the invention used in this particular machine. In the illustrated machine, the glass is drawn upwardly as a ribbon 1 from a bath 2 of molten glass, the bottom of the ribbon being stabilized by a draw bar 3. The ribbon of glass is drawn upwardly by a drawing machine 4 which includes a succession of pairs of drawing rollers. FIG. 1 shows only the bottom pair of drawing rollers, 5 and 5'. The other pairs of drawing rollers are located higher up in the drawing tower.

Beneath the rollers 5 and 5 there are further pairs of rollers 6 and 6', 7 and 7'. In the event of the glass ribbon breaking, these further rollers serve, as will be explained hereafter in more detail, to hold the lower part of the drawn glass ribbon and thereby prevent it from falling to the bottom of the drawing chamber, where it would cause serious disturbances and even require stopping of the drawing machine.

Under the drawing machine 4 is the drawing chamber 8 which is made as gas-tight as possible so as to create a zone in which temperature conditions suitable for the formation of the glass ribbon can be maintained. The drawing chamber 8 is bounded transversely by L blocks 9 and 9' which are located very near to the surface of the molten glass bath 2, and by walls 10 and 10 which connect the upper part of the L blocks with the base of the drawing machine 4. At the top of the drawing chamber 8 there are catch pans l2 and 12' which constitute the bottom of the drawing machine 4.

The molten glass bath 2 is held in a tank into which the molten glass feeds from a glass melting furnace (not shown).

The tank is formed of a bottom 13, wall 14 remote from the glass melting furnace, and crown 15.

In order to ensure rapid cooling of the faces of the freshly drawn glass ribbon, coolers 16 and 16, through which a fluid coolant such as water is circulated, are normally provided, one on each side of the glass ribbon.

. In proximity to the meniscus, where the glass ribbon is drawn from the molten glass bath, there are provided edge rolls, as commonly employed in the Pittsburgh process, for gripping the margins of the drawn glass ribbon. One part of edge rolls 17 and 17' is shown in each of FIGS. 1 and 2. The edge rolls are driven by a drive mechanism 17a (FIG. 2) located externally of the drawing chamber.

A pair of electrodes 18 and 18 is installed, with the electrode extremities close to opposed faces of one margin of the glass ribbon. Another pair of electrodes is installed at the other side of the chamber in a similar position with respect to the opposite margin of the ribbon. Each pair of electrodes is installed close to the respective pair of edge rolls. However, while this is the preferred position, it is not critical. Each pair of electrodes is connected by conductor 19 to an amplifier 20 powered by a voltage source 21.

If the glass ribbon should buckle, the glass will come into contact with one of the electrodes and electric current will flow from the electrode to ground via the glass itself and the edge roll mechanism situated just below the contacted electrode. When a current flow through one of the electrodes due to contact of such electrode by the glass, the signal constituted by this current flow is amplified and is transmitted via a conductor 22 to a central monitor 23, which can be of a known type and comprises, for example, an audible warning device 24 and indicator lamps 25.

The amplifier 20 is also connected, via a conductor 26, to an automatic control device, which includes the rollers 6 and 6 and 7 and 7', for gripping the lower part of the glass ribbon and preventing it from falling to the bottom of the drawing chamber. The rollers 6' and 7 are mounted for movement either toward or away from the glass ribbon 1. The rollers are carried by crank levers 27 and 27', respectively, which are pivotable about respective parallel horizontal axes 28 and 28'. The levers are interconnected by a bar 29 so as to move in unison.

The movement of the pair of crank levers 27 and 27 is effected by a hydraulic or pneumatic piston and cylinder unit 30 installed outside the drawing machine, e.g., on a bracket secured to the wall of the drawing chamber or drawing tower, as shown. The longer arm of crank lever 27 extends through an opening 31 in the wall of the drawing machine and is connected to the piston of the piston and cylinder unit 30. In order to reduce the force required to displace the rollers 6' and 7'., counterweights 32 are provided on the actuating arms of the crank levers.

When a signal is applied to the amplifier 20, from one of the electrodes 18 and 18', the amplified output signal passing through conductor 26 operates a control unit 33 which, via lines 34 and 34', actuates valves 35 and 35 in fluid flow lines 36 and 36' connecting one side or the other of the piston and cylinder unit 30 with a pressurized fluid supply source 37. The amplifier output signal actuates the valve so that the pressurized fluid flows in the direction indicated by the arrows, causing downward movement of the piston and clockwise pivotal motion of the crank levers 27 and 27' so that the rollers 6' and 7' become firmly pressed against the glass ribbon.

Each pair of electrodes, i.e., the electrodes 18 and 18' and the pair of electrodes (not shown) located at the other side of the drawing chamber 8 is mounted to extend through the adjacent wall of the drawing chamber in such a way that the electrodes can be positioned after the drawing machine has been set in operation. The electrode mountings include an adjustment mechanism (not shown) such as a simple screw mechanism, permitting the spacing of the electrodes from the vertical drawing plane to be varied, which may be desirable when the thickness of the drawn glass is intentionally varied.

Each of the electrodes forms part of an assembly as shown in FIG. 3 for the assembly incorporating electrode 18. The electrode is there shown to be in the form ofa cylindrical rod of a nickel steel alloy. This rod is formed with an axial socket 38 at one end for the reception of a conductor lead. The electrode is enveloped over the greater part of its length by an oxidation resistant steel tube 39 which is insulated from the electrode by a porcelain insulating sleeve 40. The root end portions of the electrode and the tube 39 are accommodated in a nylon clamping block 41 are held therein by respective screws (not shown) in threaded engagement with radial holes 41' in the block. The porcelain sleeve is positively held against axial displacement with respect to the tube 39 by a locating ring 42 which abuts the outer end of the sleeve and is soldered to the electrode.

Reference is now made to FIG. 4 which shows indicator and control circuitry which may be used in the indicator and control system of the machine which has been described with reference to FIGS. 1 to 3. The system comprises a transistorized amplifier 43 incorporating two npn-type silicon transistors T and T and resistors R R R and R The amplifier is connected via a bridge 44 to an alternating voltage source 45. The source 45 supplies a 24 Volt output while the direct voltage output from the bridge is Volts and is smoothed by a capacitor C.

Electrodes 46 and 46', the extremities of which are located close to the opposite faces of, and adjacent one edge of, glass ribbon 47 in a drawing chamber 48, are connected to amplifier 43 through resistance R,. A second pair of electrodes 49 and 49' is similarly connected to a second amplifier (not shown) identical with the one illustrated If the glass ribbon 47 should buckle, the glass will come into contact with one or more of the electrodes. If the glass contacts either of the electrodes 46 and 46', the amplifier input will be connected to ground via the glass itself and the edge roll mechanism situated a little below these electrodes, as previously described with reference to FIG. 1.

The resistors R and R the latter of which is variable, form a voltage divider which applies a required voltage to the base of transistor T The emitter of transistor T is connected to the base of transistor T and the collector of the transistor is connected to the coil of a relay 50. When T becomes conductive, a closed circuit is formed between the relay coil and the output of bridge 44 to deliver current to the coil. When the relay 50 is energized, a switch 51 closes and switches on a warning and control mechanism indicated generally at 52. The warning mechanism includes an audio and visual alarm and corresponds to the monitor 23 of FIG. 1. The control mechanism is similar to that of FIG. 1 and includes a movable roller which moves under solenoid control into gripping contact with the glass ribbon at the bottom end of the tower section of the drawing machine.

- The relay 50 may additionally actuate holding relays in the warning and control circuits, the purpose of these holding relays being to keep the circuit closed after opening of the contact between the electrode and the glass. The holding relays can be reset manually.

FIG. 5 shows another amplifier circuit embodiment including a thyristor T as the active element designed to give greater thermal stability and to avoid disturbance by parasitic electrical impulses.

If the glass ribbon comes into contact with either of the electrodes 46 and 46', the triggering circuit of thyristor T is grounded via the glass itself and the edge roll mechanism situated a little below these electrodes. This circuit incorporated a Zener diode 53. Current is transmitted through this diode only when the potential at point 54, determined by the time constant R C reaches the threshold value of the Zener diode such that any induced parasitic electrical impulses are rendered ineffective. The potential applied to the gate of the thyristor, as determined by the capacitor C and resistor R is increased by the current supply via the Zener diode 53 to the point at which the thyristor fires and causes energization of relay 50 with results similar to those described with reference to FIG. 4. The thyristor serves to hold the relay 50 energized and when the cause of the buckling of the glass ribbon has been determined and the drawing of the glass is resumed, the circuit can be reset by depressing the contact breaking button 55.

FIGS. 6, 7 and 8 illustrate a further embodiment in which the glass ribbon 56 is drawn upwards through the drawing chamber 57 of a drawing machine. Only part of the drawing chamber, formed by transverse wall 58 and 59 and side wall 60, appears in FIG. 6.

Pairs of edge rolls are provided as in the machine described with reference to FIGS. 1 and 2, for retaining the margins of the drawn glass ribbon near the meniscus, where the ribbon is drawn from the bath, of molten glass. One pair of such rollers, 61 and 61 is shown, together with their drive mechanism 62.

Slightly above the edge rolls 61 and 61 and in proximity to respectively opposite faces of the same edge of the glass ribbon, there is disposed a pair of electrodes 63 and 63' in the form of plates disposed parallel to the opposed faces of the ribbon. A similar pair of electrodes is similarly located adjacent the opposite edge of the ribbon. The electrodes of each pair are located quite close to the glass ribbon path, but with a sufficient spacing to avoid contact of the glass with either electrode in the event that the ribbon begins to buckle.

The plates 63 and 63', which may be formed of refractory steel, are carried by respective heavy section stems 64 and 64, which may be made of the same material. These stems are in turn supported by respective tubes 65 and 65 extending through the wall of the drawing chamber. Those tubes also support smaller diameter tubes 66 and 66', respectively, which extend axially along the interiors of the respective tubes and 65 and are connected to respective flexible pipes 67' through which cooling air is supplied. The inner tubes .66 and 66' are sealed into the wider tubes 65 and 65' by end plugs 67 and the cooling air flows through the inner tubes 66 and 66 into the interior of the outer tubes 65 and 65' via holes 68 and 68' in the inner tubes, and then to the atmosphere via openings 69 and 69' in the outer tubes. This circulation of air keeps the inner and outer tubes at a sufficiently low temperature to ensure that they do not become deformed. The plate elec trodes 63 and 63' are not however appreciably cooled by the air circulation. The electrodes are connected to control circuitry, as will hereafter be described, by conductors 70 and 70'.

It is advantageous to provide the plate electrodes and carrying stems with protective layers 71 and 72, respectively, as shown in FIG. 7 so as to protect these components from oxidation and corrosion. Alternatively the components can be formed from very high melting glass, or from a carbide, nitride or silicide.

The parts of the glass ribbon 56 which face the plate electrodes 63 and 63 are at a temperature such that the glass is electrically conductive and by reason of the large mass of the bath of molten glass from which the glass ribbonis drawn, the glass ribbon can be considered as a grounded conductor. The plate electrodes 63 and 63' and the glass ribbon 56 thus together form two electrical capacitors, one capacitor being formed by electrode 63 and the glass ribbon, and the other capacitor being formed by the glass ribbon and the electrode 63'. The gaseous medium forming part of the atmosphere in the drawing chamber 57 and occupying the spaces between the glass ribbon and the electrodes constitutes the dielectric for these capacitors.

Consequently the occurrence of a buckle or wave in the glass ribbon can be detected by detecting changes in the capacitances of the said capacitors. Thus, when a wave forms in the glass ribbon 56, the glass approaches one electrode and moves away from the other electrode and in consequence the capacitance of the capacitor formed by the glass ribbon and the said one electrode increases and the capacitance of the other capacitor decreases.

The capacitance variations can be measured by an instrument 73 to which the electrodes are connected by the conductors 70 and 70', as shown in FIG. 8. The instrument 73 emits a signal when some variation, preferably a variation above a predetermined value in order to avoid improper functioning, occurs on either side of the ribbon. The signal may, for example, be proportional to merely a function of the difference between the variations of the capacities of the two capacitors. Circuitry for producing such a signal is abundantly well known in the electronic art.

The output signal is conducted by line 74 to the input side of an amplifier of the type shown in FIG. and the output side of the amplifier is connected to a monitor hand, via conductors 77 a high frequency alternating voltage produced by agenerator 78 which is itselfa generator from the said supply network. Advantageously, the capacitance of the said capacitors are measured by submitting the capacitors to a high frequency alternating voltage because any increasing. of the frequence causes a decreasing of the impedance just as it occurs in the case of an increasing of the capacitance. Since the capacitance or, more precisely, the impedance of this capacitance is measured by measuring the intensity of the current traversing the capacitance or the fall in the electrical voltage caused by this impedance, the precision of the measure is thus increased because higher intensities or falls in electrical voltage are measured when using high frequency alternating voltage.

Advantageously, the instrument 73 comprises a preamplifier element which is fed.by conductors 75 in order to amplify the signal emitted by the measuring element of the instrument 73.

Another embodiment is shown in FIG. 9 where the glass ribbon 79 is being drawn upwardly through a drawing chamber defined in part by walls 80, 81 and 82. If the ribbon should buckle, this induces variations in the gas pressure in a tube from which gas continuously discharges at a point located near to the correct path of the ribbon. To this end, a pair of tubes 83 and 83 is provided for discharging gas against opposed faces of the glass ribbon at positions just above the conventional edge rolls 84 and 84. A similar pair of tubes (not shown) is provided in the same way at the opposite margin of the glass ribbon.

The discharge end portions 85 and 85' of the tubes 83 and 83 are located at a sufficient distance from the opposed faces of the glass ribbon to ensure that when a buckle or wave commences to form, this phenomenon will be detected and the ribbon will be gripped before the glass ribbon actually comes into contact with the discharge ends 85 and 85' of the tubes. In this way fouling of the tubes is avoided. The gas discharged tubes 83 and 83' are supported by outer coaxial tubes 86 and 86', respectively, extending through wall 82 of the drawing chamber. The inner ends of the outer supporting tubes 86 and 86 are sealed to the respective gas discharge tubes 83 and 83' while the outer ends of such supporting tubes are sealed by respective plugs 87 and 87' to pipes 88, 89 and 88' and 89', respectively through which a fluid coolant, e.g., water or air, is fed for cooling the air or other gas which is supplied through tubes 83 and 83.

Within the tubes 83 and 83' there are respective local flow restrictors 90 and 90' which cause a pressure drop so that the gas in the portions of the tubes 83 and 83' located downstream of the flow restrictors are at the lower pressure. The tubes 83 and 83' are fed by a common supply pipe Q1 via a pressure regulator 92 which maintains a constant gas feed pressure. On the low pressure side of the flow restrictors, the tubes 83 and 83 are connected by respective tubes 93 and 93' to a measuring instrument 94 which advantageously is situated outside the drawing chamber.

If the glass ribbon begins to buckle, the ribbon approaches the gas discharge end of one of the tubes 83 and 83' and moves away from the gas discharge end of the other of such tubes. In consequence, the gas pressure in the portion of the one tube which is located downstream of its flow restrictor 90 and 90 increases, whereas the pressure in the corresponding portion of the other tube decreases. These variations of pressure are communicated via tubes 93 and 93' to the measuring instrument 94, which may be of a known type, which emits a signal, for example a voltage, which may be proportional to, or a function of the difference between the pressure variations. This signal is transmitted via a conductor (not shown) to the input side of an amplifier, similar to the amplifier shown in FIG. 5, and that amplifier is connected to a warning device and to a device for actuating the gripping rollers, such as roller 6' and 7 shown in FIG. 1.

In another embodiment (not shown) of the invention, very similar to the embodiment shown in FIG. 9, the occurrence of a wave in the drawn glass ribbon is detected by detecting variations in the rate of discharge of fluid rather than variations in the pressure of the discharged fluid.

Reference is now made to FIG. which shows part of a Libbey-Owens type glass drawing machine provided with one embodiment according to the invention. In the type of glass drawing machine referred to hereabove, a sheet 95 is continuously drawn from a mass of molten glass 96 contained in a commonly called draw pot 97; this draw pot being continuously replenished with molten glass coming from a tank furnace (not shown). As it is well known, the temperature of the mass of molten glass 96 contained in the draw pot 97 is controlled, at least partially, by means of burners (not shown) located below the draw pot 97 and hot gases, generally issuing from the furnace and passing inwardly through the passageway 98. The sheet 95 is drawn preferably in a vertical plane initially and subsequently deflected horizontally over a bending roller 99 and further carried through an annealing lehr 101 which is partially shown in FIG. 10. Arranged above the draw pot 97 are cover or lip tiles 102 and 102' which tend to force any heat current present at that point downwardly toward the surface of the molten glass 96. Coolers 103 and 103' are disposed relatively close to the surface of the molten glass from which the sheet is drawn and absorb sufficient heat to permit the drawing of a good sheet of glass. Edge treating means in the form of knurled rollers 104 and 104' are also provided adjacent the surface of molten glass 96 to maintain the sheet to width. A pair of electrodes 105 and 10S, e.g., similar to the electrodes shown in FIG. 3, is installed with the electrode extremities close to opposed faces of one margin of the glass sheet 95. Another pair of electrodes is installed at the other side of the chamber in a similar position with respect to the opposite margin of the said glass sheet. In a preferred position, each pair of the said electrodes is installed close to the said respective knurled rollers 104 and 104'. Each pair of electrodes, as already shown in the FIG. 1, is connected by conductor 106 to an amplifier 107 powered by a voltage source 108. The amplifier 107 is connected, via a conductor 110 to a central monitor 111, which may be similar to the monitor shown in FIG. 1 and comprise, for example, an audible warning device 113 and indicator lamps 112. The amplifier 107 is also connected, via a conductor 109 to an automatic control device, which includes, close to opposed faces of each margin of the glass sheet 95, edge rollers 114 and 114' which do not extend on the entire width of the glass sheet 95 and serve, when a break of the glass sheet occurs, to grip the glass sheet and to prevent it from falling toward the bottom of the drawing machine. For

this purpose, a roller of each pair, e.g., the roller 114', is mounted for movement either toward or away from the glass sheet 95. For example, the said movable roller 114 may be carried by a crank lever, one arm 115 of which, located in the drawing chamber, is connected to the roller 114 while the other arm 116, located outside of the drawing chamber, is connected to, e.g., a jack 118 permitting to move the said roller and which may be installed on a bracket 119 secured on the side wall 120 of the drawing chamber. The said crank lever is pivotable about an horizontal axle 117 which may be fixed, for example, by means of a bearing located in the side wall 120. An embodiment according to the invention, e.g., similar to that shown in FIG. 10, may also be used in drawing machines nearly similar to the Libbey- Owens drawing machines, however comprising a deep draw pot, as it is the case in other known processes.

Reference is now made to FIG. 11 which shows another type of indicator and its assembly. The glass ribbon 121 is drawn from a bath of molten glass through a drawing chamber 122, shown only partially and laterally closed by side walls 123, 124 and 125. A little above the edge rolls (not shown), e.g., similar to the edge rolls 17 and 17', illustrated in FIG. 1, a pair of switch arms 126 and 126' is installed so that the switch arm extremities which are located in the drawing chamber 122, are close to opposed faces of one margin of the glass ribbon 121. Another pair of switch arms is installed at the other side of the chamber in a similar position with respect to the opposite margin of the ribbon. These switch arms, e.g., made of a refractory material as quartz or pure alumina, are pivotably mounted by means of pivots 127 and 127 fixed on plates 128 and 128', e.g. made of metal; these plates being fixed on a steel section 129 which may be fastened on the outer face of the drawing chamber wall 124 by fixing means 130 and 130 as gudgeons and screw-nuts. In order to make it possible to locate the said pivots Z27 and 127 out of the drawing chamber for preventing them from being submitted to a high temperature, holes 131 and 131, through which the switch arms are passing, are provided in the wall 124 of the drawing chamber. The dimensions of these holes are such that they enable adequate movement of the switch arms around their respective pivot. The extremities of the switch arms 126 and 126' which are located out of the drawing chamber actuate respectively, by means of rod 138, 138' and spring 139, 139, the switches 132 and 132', fixed on the steel section 129, which, e.g., close or open an electrical circuit comprising respectively, for example, a conductor 133, 133 connected to the earth and another conductor 134, 134 connected to an amplifier, as already shown in FIG. 4. Advantageously, in order to adjust accurately the position of the switch arms in relation to the faces of the glass ribbon 121, the said switches 132 and 132 are fixed by sliding means 135 and 135 and adjusting screws 136 and 136. Moreover, in order to avoid the entry of cold air in the drawing chamber, the holes 131 and 131' are filled with material 137 as, e.g., glass wool; this material must be compressible enough to permit a rotating movement of the switch arms 126 and 126'.

If the glass ribbon 121 should buckle, the glass will come in contact with one of the switch arms 126 and 126 and will displace it. By its displacement, the switch arm will actuate one of the switches 132, 132 and an electric current will flow to ground via conductors 133, 134 and 133', 134'; this current constituting a signal which will be amplified in order to actuate an automatic control device or an indicator system as already herein described. When the glass ribbon will turn in a correct position, the switch arm will have been discplaced, will return into its starting position under the effect of the spring 139 or 139.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. In the processing of sheet glass by drawing a ribbon of glass upwardly from a bath of molten glass, a method for detecting any bucklingfo the glass ribbon, comprising the steps of: monitoring deflections experienced by the ribbon out of the vertical plane along which it is normally drawn by placing sensing components at a level near the surface level of the bath and also near, and normally out of contact witlfl opposite faces of the ribbon, near one edge thereof, and causing the components to produce an output signal in response to a change in a physical condition of the region adjacent to the components due to such deflection.

2. A method as defined in claim 1 wherein said components are caused to produce an output signal in the event of contact of the ribbon with a component located to one side of the ribbon.

3. A method as defined in claiml wherein said components are caused to produce an output signal in the event that the spacing of the ribbon from a component located on either side of the ribbon changes by more than a predetermined value.

4. A method as defined in claim 3 wherein said components are electrodes which form electric capacitors with the ribbon and produce a signal in dependence on variations in the capacitances of said capacitors.

5. A method as defined in claim 3 wherein said components direct streams of fluid against opposite sides of the ribbon and produce a signal in dependence on changes in fluid flow conditions in said conponents due to movement of the ribbon nearer to one said component located on one side of the ribbon and further away from one said component located on the other side of the ribbon.

6. A method as defined in claim 1 comprising the further step of causing the output signal to actuate a device for gripping the ribbon to prevent it falling in the event that the emission of such signal is due to breakage of the ribbon.

7. A method as defined in claim 6 wherein the signal actuates the displacement of at least one roller into contact with the ribbon to cause it to be gripped.

8. A method as defined in claim 1 wherein the processing involves drawing the glass ribbon upwardly from the bath of molten glass through a vertical tower section above a chamber in which the glass ribbon is drawn from a bath of molten glass.

9. A method as defined in claim 1 wherein the processing involves drawing the glass ribbon vertically upwardly from a bath of molten glass and then bending the ribbon over a bending roller before continuing its movement in a substantially horizontal direction. 

1. In the processing of sheet glass by drawing a ribbon of glass upwardly from a bath of molten glass, a method for detecting any buckling fo the glass ribbon, comprising the steps of: monitoring deflections experienced by the ribbon out of the vertical plane along which it is normally drawn by placing sensing components at a level near the surface level of the bath and also near, and normally out of contact with, opposite faces of the ribbon, near one edge thereof, and causing the components to produce an output signal in response to a change in a physical condition of the region adjacent to the components due to such deflection.
 2. A method as defined in claim 1 wherein said components are caused to produce an output signal in the event of contact of the ribbon with a component located to one side of the ribbon.
 3. A method as defined in claim 1 wherein said components are caused to produce an output signal in the event that the spacing of the ribbon from a component located on either side of the ribbon changes by more than a predetermined value.
 4. A method as defined in claim 3 wherein said components are electrodes which form electric capacitors with the ribbon and produce a signal in dependence on vAriations in the capacitances of said capacitors.
 5. A method as defined in claim 3 wherein said components direct streams of fluid against opposite sides of the ribbon and produce a signal in dependence on changes in fluid flow conditions in said conponents due to movement of the ribbon nearer to one said component located on one side of the ribbon and further away from one said component located on the other side of the ribbon.
 6. A method as defined in claim 1 comprising the further step of causing the output signal to actuate a device for gripping the ribbon to prevent it falling in the event that the emission of such signal is due to breakage of the ribbon.
 7. A method as defined in claim 6 wherein the signal actuates the displacement of at least one roller into contact with the ribbon to cause it to be gripped.
 8. A method as defined in claim 1 wherein the processing involves drawing the glass ribbon upwardly from the bath of molten glass through a vertical tower section above a chamber in which the glass ribbon is drawn from a bath of molten glass.
 9. A method as defined in claim 1 wherein the processing involves drawing the glass ribbon vertically upwardly from a bath of molten glass and then bending the ribbon over a bending roller before continuing its movement in a substantially horizontal direction. 